A. Field of Invention
This invention pertains to a knee bolster to be used in a motor vehicle usually in conjunction with either an airbag or shoulder belt to protect a passenger from injury during frontal-type collisions, and more particularly to a bolster which elastically saves a portion of the collision energy to provide a controlled rebound of the occupant against the seatback, such that the rebound impact forces on the occupant's head or neck are minimized.
B. Description of the Prior Art
Studies have shown that during a frontal automobile crash, an occupant first moves forward (at substantially the original speed of the automobile) with respect to the automobile's body, and then rebounds towards the seat. Thus, he can suffer serious injuries not only from the first impact but also during the second impact with the seat. This second impact is usually termed secondary collision. While occupant restraints (such as seat belts) were found to alleviate such injuries, even with protective legislation passed by several states, the public is not ready to accept these restraints because of various inconveniences to the occupants.
Alternate solutions have also been proposed, including passive restraints such as airbags and automatic shoulder belts with conventional knee bolsters. In a vehicle so equipped, the restraint acts to absorb the kinetic energy of the occupant during the primary impact so that, theoretically, the occupant would escape with little or no injuries. However, it was found that even with such restraints, some occupants were still getting injured. Further studies have shown that these injuries can be attributed to the fact that the chest restraint does not dissipate all the kinetic energy of the occupant but instead stores at least a portion of it and then reflects the stored energy back to the occupant in a semi-elastic collision during the primary impact resulting in a secondary collision against the back of the seat. More particularly, it was found that since the impact between the occupant and the chest restraint is centered in the upper chest area, i.e. above the occupant's center of gravity, the occupant is subject to both a translation (i.e. backward) and a rotation (with the upper torso turning away from the front end of the vehicle). As a result of this rotation, the upper portion of the occupant's body (i.e. the head and the neck) impacts first during the secondary collision with the seatback. Since this part of the body is very fragile, even a minor secondary impact could result in injuries.